The present invention relates to a control system capable of coping with bus extension, and more particularly to a control system capable of coping with bus extension which is suitable for a communication apparatus in which a control system including a single CPU controls a unit apparatus which is formed by a plurality of racks so as to accommodate a plurality of channels in the unit apparatus.
In 1988, CCITT (International Telegram and Telephone Consultative Committee) recommended the application of SDH (Synchronous Digital Hierarchy) to communication apparatuses. Therefore, in recent years, research and development efforts on communication apparatuses which can be adapted to SDH have been actively undertaken in relation to both radio transmission apparatuses and wire transmission apparatuses.
Communication apparatuses adapted to SDH are required to have an increased transmission capability and an enhanced monitor/control function; i.e., such a communication apparatus must provide enhanced ease of operation, a security function, flexible services, and the like.
On the other hand, since communication protocols have been standardized in order to unify manners of operation of communication networks (i.e., since there has been a movement toward allowing connection between different systems so as to unify networks all over the world), it becomes necessary for communication apparatus to cope with such a trend. Additionally, in the TMN (i.e. Telecommunication Management Network) wherein each communication apparatus is called an NE (Network Element), it also becomes necessary for each unit apparatus to be handled as a single NE so that the network can be operated efficiently.
In a general communication apparatus adapted to SDH, a plurality of channels (i.e., transmission paths each having a predetermined unit transmission capacity) are accommodated in a single NE so as to increase the transmission capacity. In such a communication apparatus including a plurality of channels, a plurality of racks are sometimes combined together to form one NE.
In the communication apparatus as described above, in particular, when each NE is formed by a plurality of racks, it is required not only to suppress an increase in the scale of hardware, but also to efficiently construct a monitor/ control system for monitoring and controlling channels, taking into account functions to be provided and equipment cost.
FIG. 50 is a diagram showing an example of a communication apparatus in which a plurality of racks form a single NE. In FIG. 50, numeral 100 denotes a communication apparatus which is constructed as a unit through the use of three racks 101-1 to 101-3. In each of the racks 101-1 to 101-3 shown in FIG. 50, numeral 102 denotes a transmission section (TX) for transmitting data in the form of radio signals; numeral 103 denotes a reception section (RX) for receiving data in the form of radio signals; and numerals 105 and 106 denote shelves, each shelf comprising two channels.
Thus, twelve channels in total are accommodated in the shelves 105 and 106 of the three racks 101-1 to 101-3. Among the twelve channels, one of the channels accommodated in the shelf 105 of the rack 101-1 can be used as a spare channel (PROT) while the remaining eleven channels can be used as communication channels (ch1 to ch11).
Numeral 104 denotes a common section (COM) provided in the rack 101-1. The common section 104 includes an unillustrated equipment CPU which serves as a monitor/control section 104a for monitoring and controlling each of the channels in the three racks 101-1 to 101-3.
In recent years, the above-described equipment CPU, which functions as the monitor/control section 104a, has been designed on the basis of a multi-CPU configuration so as to realize a monitoring/control system that operates at high speed and that provides improved functions.
When the above-described racks 101-1 to 101-3 are dispersed spatially, the following method may be employed for monitoring and controlling the channels. That is, a CPU is provided for each channel so as to collect information, and information of the entire apparatus is collected by the common section 104 through a serial communication such as an HDLC between the CPU and the common section 104. Particularly, when the number of items to be monitored and/or controlled is small, monitoring and controlling can be performed through transmission of information via electrical contacts.
However, even when the above-described measure is employed, problems will arise in the case where the communication apparatus as shown in FIG. 50 is applied to an apparatus, such as an SDH-adapted communication apparatus, which is required to have enhanced monitor/control functions. That is, when serial communication is performed between the CPU provided for each channel and the common section 104, the hardware cost of the channel sections increases, and the processing load of the CPU provided in the common section 104 also increases. Moreover, in the information transmission system utilizing electric contacts or the like, the amount of transmissible information is limited to a low level, so that it becomes difficult to form a monitor/control system.
Further, it is possible to employ a multi-CPU configuration and to mutually connect a plurality of racks by extending the CPU bus. In this case, information regarding devices, which is input through the CPU bus, is collected by the common section 104, which performs monitoring and controlling on the basis of the thus-collected information. In this case, however, the following problems will arise.
(1) The number of transmission signal lines is considerably large (e.g., 40 or more, including address lines, data lines, and control lines). PA1 (2) Transmission speed is high (approximately 10 MHz when a 16-bit CPU is used). PA1 (3) Bus control (tri-state control and the like) becomes complicated due to increased transmission distance. PA1 (4) Termination (impedance matching) becomes difficult due to increased transmission distance. PA1 (5) Electric levels must be changed from those suitable for TTL/CMOS to those suitable for long distance transmission.
Therefore, there have been no cases in which spatially separated racks have been connected together through extension of a CPU bus.